Indirect tire pressure monitoring systems and methods

ABSTRACT

Embodiments relate to indirect tire pressure monitoring systems (TPMSs) and methods that utilize anti-lock braking system (ABS) signals. In embodiments, information from the ABS Hall signal is obtained in analog form, before pulse forming. The information can be analyzed for a resonance frequency within the ABS sensor. In some embodiments, the digitized information can be modulated onto the conventional ABS wheel speed clock signal for transmission to and analysis by the indirect TPMS electronic control unit (ECU). According to embodiments, additional information about higher-order harmonics of the wheel rotation can be provided to the TPMS ECU, which can then calculate a more accurate estimation of tire pressure while reducing warning latency.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/284,043 filed on Oct. 28, 2011 and claims the benefit of the prioritydate of the above U.S. application, the contents of which are hereinincorporated in its full entirety by reference.

TECHNICAL FIELD

The invention relates generally to indirect tire pressure monitoring andmore particularly to the use of analog Hall signals from wheel speedsensors for indirect tire pressure monitoring.

BACKGROUND

There are two general approaches to monitoring the pressure in vehicletires: direct and indirect. Direct tire pressure monitoring systems(TPMSs) typically comprise a wheel module having one or more sensors andelectronics mounted in or to the tire to directly measure the tire'spressure and wirelessly transmit measurement data to the vehicle.

Indirect TPMSs generally utilize information from other vehicle sensorsand/or systems to indirectly estimate a tire's pressure without TPMSsensors or electronics being located in the tire. Indirect TPMS isattractive because it can be more cost-efficient than direct TPMS. Oneconventional indirect TPMS uses wheel speed signals from the anti-lockbrake system (ABS). For a typical passenger vehicle having four tires,the indirect TPMS compares the four wheel speed signals to determinewhether a wheel is rotating faster because of a loss of pressure andrelated decreased diameter. One drawback to some of these indirectsystems is that the systems cannot detect whether all wheels have lostpressure over time because the values are compared.

Further, the quality of the signals from the ABS or other vehiclesystem(s) is important for indirect TPMS. Conventional indirect TPMStypically use digital signals from the ABS representing the clockgenerated by a rotating pole wheel. The digital signals are derived froman analog Hall signal by detecting the minimum and maximum values of thesignal and determining the zero-crossing points. Unfortunately, valuableinformation about resonance of the tire and higher-order harmonics onthe clock signal is lost by using the derived digital signals.Conventional systems therefore must attempt to recover higher-orderharmonics in the ABS clock signal, though with only limited performanceresults.

Therefore, there is a need for improved systems and methods for indirecttire pressure monitoring.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 is a block diagram of a system according to an embodiment.

FIG. 2 is a signal modulation diagram according to an embodiment.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

Embodiments relate to indirect tire pressure monitoring systems (TPMSs)and methods that utilize anti-lock braking system (ABS) signals. Inembodiments, information from the ABS Hall signal is obtained in analogform, before pulse forming. The information can be analyzed for aresonance frequency within the ABS sensor. In some embodiments, thedigitized information can be modulated onto the conventional ABS wheelspeed clock signal for transmission to and analysis by the indirect TPMSelectronic control unit (ECU). According to embodiments, additionalinformation about higher-order harmonics of the wheel rotation can beprovided to the TPMS ECU, which can then calculate a more accurateestimation of tire pressure while reducing warning latency, therebyproviding a more robust system that balances provision of early warningswith false alarms.

Referring to FIG. 1, a block diagram of ABS sensor circuitry 100 isdepicted. Circuitry 100 includes an analog portion 102 and a digitalportion 104 coupled by an analog-to-digital (ADC) converter 106. Analogportion 102 comprises one or more Hall probes 108, offset compensationcircuitry 110 and gain circuitry 112. Digital portion 104 comprisesmaximum/minimum detection circuitry 114, zero-crossing detectioncircuitry 116, frequency analysis circuitry 118, analysis of harmonicscircuitry 120 and pulse forming circuitry 122. Frequency analysiscircuitry 118 and analysis of harmonics circuitry 120 form part of anindirect TPMS 124.

The addition of frequency analysis circuitry 118, which in an embodimentcomprises Fast Fourier Transform (FFT) circuitry, and analysis ofharmonics circuitry 120 to ABS sensor circuitry 100 enables extractionof wheel speed and resonance frequency information as well additionalinformation, for example information related to center frequency,Q-factor and higher-order resonances from the Hall signal, as comparedto conventional indirect TPMS approaches. In general, wheel speedcorresponds to the first order frequency of the signal, with the wheelspeed corresponding to a duration between pulses. In one embodiment,there are about 48 pulses per rotation, which provides good granularity.Changes in these characteristics can then be analyzed to determinewhether any are indicative of a change in the pressure of the tire.

For example, indirect TPMS 124 can detect a change in resonancefrequency of a tire. A decrease of the resonance frequency could beindicative of a lower tire pressure in the tire.

Information then can be transmitted from indirect TPMS 124 to a TPMS orvehicle ECU in several manners. In a first embodiment, information fromindirect TPMS 124 is represented in a digital frame protocol format andis modulated onto the original ABS clock signal by adapting the pulselength to the state of the related bit of the frame. Thus, the ABS wheelspeed signal is represented by the rising edge while the TPMSinformation is in the pulse duration of a sequence of pulses. Refer, forexample, to FIG. 2. In another embodiment, a separate communicationsource, such as a wired or wireless connection, can be provided betweenindirect TPMS 124 and the ECU.

Other TPMS systems can use digital ABS sensor signals, but these systemsare inferior to embodiments disclosed herein. The information used forthe resonance analysis is embedded in the point-in-time of the slopes ofthe signal. Therefore, jitter errors in this signal are a serious sourceof disturbance for TPMS performance. This jitter can be considered to bea non-constant delay between a zero-crossing of the analog signal andslope of the digitized signal. This problem arises from the permanentadaptation in minimum/maximum detection and zero-crossing detectionduring operation. Therefore, this jitter error is disclosed in ABSsensor datasheets. Those implementing indirect TPMS seek low jitter, anduse of the analog signal for indirect TPMS, as disclosed herein, makesmoot the jitter issue, providing a significant advantage overconventional approaches.

Various embodiments of systems, devices and methods have been describedherein. These embodiments are given only by way of example and are notintended to limit the scope of the invention. It should be appreciated,moreover, that the various features of the embodiments that have beendescribed may be combined in various ways to produce numerous additionalembodiments. Moreover, while various materials, dimensions, shapes,configurations and locations, etc. have been described for use withdisclosed embodiments, others besides those disclosed may be utilizedwithout exceeding the scope of the invention.

Persons of ordinary skill in the relevant arts will recognize that theinvention may comprise fewer features than illustrated in any individualembodiment described above. The embodiments described herein are notmeant to be an exhaustive presentation of the ways in which the variousfeatures of the invention may be combined. Accordingly, the embodimentsare not mutually exclusive combinations of features; rather, theinvention may comprise a combination of different individual featuresselected from different individual embodiments, as understood by personsof ordinary skill in the art.

Any incorporation by reference of documents above is limited such thatno subject matter is incorporated that is contrary to the explicitdisclosure herein. Any incorporation by reference of documents above isfurther limited such that no claims included in the documents areincorporated by reference herein. Any incorporation by reference ofdocuments above is yet further limited such that any definitionsprovided in the documents are not incorporated by reference hereinunless expressly included herein.

For purposes of interpreting the claims for the present invention, it isexpressly intended that the provisions of Section 112, sixth paragraphof 35 U.S.C. are not to be invoked unless the specific terms “means for”or “step for” are recited in a claim.

What is claimed is:
 1. A sensor comprising: sensing circuitry to sense awheel speed; an analog to digital converter coupled to the sensingcircuitry to convert an analog signal into a digital signal; frequencyanalysis circuitry to receive the digital signal from the analog todigital converter and to derive frequency information for indirect tirepressure monitoring; transmission circuitry to transmit the frequencyinformation for indirect tire pressure monitoring from the sensor to anelectronic control unit.
 2. The sensor of claim 1, further comprisingdetection circuitry to determine signal crossings and to generate apulse signal based on signal crossings, and wherein the transmissioncircuitry is configured to modulate the frequency information into thepulse signal.
 3. The sensor of claim 2, wherein the digital signal fromthe analog to digital converter is provided to the frequency analysiscircuitry and the detection circuitry in parallel.
 4. The sensor ofclaim 3, wherein the detection circuitry and the frequency analysiscircuitry are arranged in parallel signal paths.
 5. The sensor of claim4, wherein the frequency analysis circuitry comprises at least FourierTransformation circuitry.
 6. A sensor comprising: sensing circuitry tosense a wheel speed; an analog to digital converter coupled to thesensing circuitry to convert an analog signal into a digital signal;harmonics analysis circuitry to receive the digital signal from theanalog to digital converter and to derive harmonics information forindirect TPMS; transmission circuitry to transmit the harmonicsinformation for indirect TPMS from the sensor to an electronic controlunit.
 7. The sensor of claim 6, further comprising detection circuitryto determine signal crossings and to generate a pulse signal based onsignal crossings, and wherein the transmission circuitry is configuredto modulate the harmonics information into the pulse signal.
 8. Thesensor of claim 7, wherein the detection circuitry and the harmonicsanalysis circuitry are arranged in parallel signal paths.
 9. The sensorof claim 6 further comprising frequency analysis circuitry, wherein theharmonics analysis circuitry is coupled to the frequency analysiscircuitry.
 10. A system comprising: a sensor to provide a wheel speedsignal; an electronic control unit to receive the wheel speed signalfrom the sensor; an indirect tire pressure monitoring system (TPMS) toderive tire pressure information, wherein the sensor comprises at leasta part of a digital TPMS analysis circuitry of the indirect TPMS. 11.The system of claim 10, wherein said part of the digital TPMS analysiscircuitry includes a frequency analysis circuitry.
 12. The system ofclaim 10, wherein said part of the digital TPMS analysis circuitryincludes a harmonics analysis circuitry.
 13. The system of claim 10,wherein the sensor further comprises detection circuitry to determinesignal crossings and to generate a pulse signal based on signalcrossings, and wherein the sensor further comprises transmissioncircuitry to modulate information generated by said part of the digitalTPMS circuitry into the pulse signal.